This invention relates generally to gas turbine engine nozzles and more particularly, to methods and apparatus for supplying cooling fluid to turbine nozzles.
Gas turbine engines include combustors which ignite fuel-air mixtures which are then channeled through a turbine nozzle assembly towards a turbine. At least some known turbine nozzle assemblies include a plurality of nozzles arranged circumferentially. At least some known turbine nozzles include a plurality of circumferentially-spaced hollow airfoil vanes coupled by integrally-formed inner and outer band platforms. More specifically, the inner band forms a portion of the radially inner flowpath boundary and the outer band forms a portion of the radially outer flowpath boundary
At least some known turbine nozzle airfoil vanes are hollow and include a cavity defined therein. At least some known airfoil vane cavities are partitioned into a leading edge cooling passage, a center passage, and a trailing edge passage. Cooling air is supplied to a manifold that extends circumferentially within the engine and around the turbine nozzle outer bands. The airflow is directed radially inwardly through a plurality of distribution ports that are formed integrally with the manifold. Specifically, the distribution ports are circumferentially-spaced about the manifold such to facilitate supplying cooling air to a respective turbine nozzle vane. More specifically, known distribution ports are defined by a substantially planar radially inner surface that extends across the port to an annular sidewall. To facilitate distributing the cooling airflow across the turbine nozzle airfoil vane cooling passages, known distribution ports include a plurality of openings that extend through the distribution port sidewall. Accordingly, the openings are oriented approximately ninety degrees from the distribution port radially inner surface.
During operation, airflow channeled to the distribution ports is forced radially inward towards the nozzle cavities through the distribution port openings. The airflow entering the distribution ports impinges against the radially inner surface of the ports and is changed in flow direction through the port openings. However, as the airflow changes flow direction, turbulence and pressure losses are generated. Moreover, the turbulence and pressure losses may adversely effect cooling airflow supplied to the airfoil vane cavity center cooling passage. Over time continued operation with decreased cooling of the center cooling passage, may limit a useful life of the turbine nozzle.